Okay, thank you for your response. I guess there is no chance to get my savegames back...
Unfortunately I can't reproduce the bug and don't have this crash report.

Yesterday I updated Factorio to 15.23 and I played some hours with exisiting savegames and everything was fine. Today I played some hours with the same savegame and after 2 hours of gaming the game crashed while auto saving. After restarting factorio I tried to load the autosave savegames, but each ...